Muscles in health and disease

Question 1

What % of body mass are muscles

Answer 1

40

Question 2

Apart from movement, what function do muscles have

Answer 2

Store of intracellular ions like potassium

Important for heat production

Question 3

What happens if there is damage to a single motor neurone

Answer 3

Affects all muscle fibres innervated by that neuron
80-90% of mass will be lost within the month
Remaining motor neurones will sprout and synapse with denervated fibres

Question 4

What determines the fibre type when re-innervation is occuring

Answer 4

Primary motor neurone

Question 5

What happens when remaining motor axons sprout to innervate denervated fibres

Answer 5

The motor units enlarge and fibres become grouped

Question 6

In terms of muscles, why may a baby suffer from infantile hypotonia

Answer 6

Fibres and small and round wtih a few massivelly hypertrophic fibres

Question 7

Describe the underlying pathophysiology of infantile myopathic hypotonia

Answer 7

• Disproportion between the 2 muscle fibres types
• Type 1 fibres which are usually the large type appear small
• Type 2 fibres which are usually smaller are normal to larger in diameter

Question 8

What respiration do the 2 types of muscle fibres undergo

Answer 8

Type 1= aerobic

Type 2= both

Question 9

Which fibre type stains darker and why

Answer 9

Type 2

ATPase demarks fibres with lots of ATPase, and as anaerobic resp less ATPase

Question 10

How may muscle disorders be diagnosed

Answer 10

Biopsy

EMG

Question 11

Name 2 inflammatory myopathies

Answer 11

Polymyositis

Dermatomyositis

Question 12

What is dermatomyositis

Answer 12

An autoimmune disorder associated with microbial infection resulting in proximal muscle weakness

Question 13

What biochemistry results may be seen in dermatomyositis

Answer 13

Elevated serum creatine kinase

Question 14

What would an EMG of somebody with dermatomyositis show

Answer 14

Irritability

Question 15

What would a biopsy of somebody with dermatomyositis show

Answer 15

Variation in fibre size
Central nuclei
Necrosis and regeneration
Infilitrate of inflammatory cells

Question 16

What lymphocytes invade in dermatomyositis

Answer 16

CD8 positive cells

Question 17

What inflammatory cells are seen in dermatomyositis

Answer 17

CD8 positive cells

macrophages to remove necrotic fibres

Question 18

What is the most obvious physical sign of dermatomyositis

Answer 18

Rash– purple and streaky

Heliotrope rash over eye with oedema

Question 19

What is subcutaneous calcification

Answer 19

Autoimmune connective tissue disease resulting in calcification of muscles and skin

Question 20

How may subcutaneous calcification be treated (3)

Answer 20

• Corticosteroids
• Azathioprine
• Methotrexate

Question 21

Describe the course of corticosteroids prescribed for subcutaneous calcification

Answer 21

• High dose 1mg/kg day

- Maintained until creatine kinase normal

Question 22

What is the 5 and 8 year survival of subcutaneous calcification

Answer 22

5 year= 80%

8 year= 73%

Question 23

What causes death in subcutaneous calcification

Answer 23

Malignancy, infection, pulmonary involvement

Question 24

What are the signs and symptoms of inclusion body myositis

Answer 24

Muscle weakness, specifically in finger and wrist flexors, shoulder abductors and knee extensors
Associated polyneuropathy, dysphagia and loss of quadriceps reflex

Question 25

What is the most common muscle disease of the elderly

Answer 25

Inclusion body myositis

Question 26

How do fibres appear in inclusion body myositis

Answer 26

Empty vacuoles and clumps of cellular material containing amyloid like material

Question 27

What structures are found in the filamentous inclusion in inclusion body myositis

Answer 27

``` Beta amyloid Hyperphosphorylated tau Apolipoprotein E Presenilin 1 Prion protein ```

Question 28

What are muscular dystrophies

Answer 28

Progressive genetically linked degenerative myopathies

Question 29

Name some x-linked muscular dystrophies

Answer 29

- Duchenne and Becker muscular dystrophies - Limb girdle muscular dystrophy - Emery- Dreifuss muscular dystrophie

Question 30

Name some autosomal recessive muscular dystrophies

Answer 30

Limb girdle muscular dystrophy | Emery-Dreifuss muscular dystrophy

Question 31

Describe what Duchenne MD is

Answer 31

Proximal muscle weakness in first 2 years of life followed by a continuous show decline Unable to walk by 7-12, death mid 20s-early 30s

Question 32

How many babies are born with Duchenne MD

Answer 32

20-30: 100,000 males

Question 33

What are the creatine kinase levels like in babies with Duchenne MD

Answer 33

Elevated

Question 34

What would a muscle biopsy of somebody with duchenne MD show

Answer 34

Fibre size variability Endomysial fibrosis Degenerating muscle fibres undergoing myophagocytosis

Question 35

What happens in the late stages of duchenne MD

Answer 35

Loss of muscle replaced by fibrotic material and fat

Question 36

What myopathies can be induced by steroids

Answer 36

Type 2 fibre atrophy

Question 37

What myopathy can be induced by statins, and in what % of patients

Answer 37

Rhabdomyolysis

Question 38

What are the features of fibromyalgia

Answer 38

- Widespread muscle pain with associated fatigue and sleep disturbance - Both sides of the body in axial skeleton

Question 39

50% of fibromyalgia patients are positive for what

Answer 39

Antipolymer antibodies

Question 40

What is the normal age and sex of fibromyalgia patient

Answer 40

``` 30-60 Majority female (80-90%) ```

Question 41

How is fibromyalgia treated

Answer 41

Tricyclic antidepressant (amitriptyline) SSRI (fluoxetine) Exercise